The Government is likely to prevail in King v. Burwell if its interpretation of the Affordable Care Act receives Chevron deference. This raises an important question: what influences when Supreme Court justices grant Chevron deference to agencies?

Prof. Bill Eskridge and I examined this question in a paper that examined all Supreme Court cases from 1984 to 2006 that concerned an agency interpretation of a statute. Our results show the justices are inconsistent in granting Chevron deference as well as other forms of deference. While the factors set forth in the case law do appear to influence deference, other variables including judicial ideology and the nature of the policy decision are also important.

These results are consistent with Justice Kennedy’s comment in yesterday’s oral argument that “it seems to a drastic step for us to say that the Department of Internal Revenue and its director can make this call one way or the other when there are, what, billions of dollars of subsidies involved here?”

We conclude that deference regimes are more akin to canons of statutory construction than to binding precedents. This suggests that Chevron may do considerably less independent work in determining the outcome of King v. Burwell than one might expect from reading the case law alone.